Evaluation of Cuban Bacillus thuringiensis (Berliner, 1911) (Bacillales: Bacillacea) isolates with larvicidal activity against Aedes aegypti (Linnaeus, 1762) (Diptera: Culicidae)

ABSTRACT

Objective: To evaluate 11 Cuban native Bacillus (B.) thuringiensis isolates in order to select one with the best larvicidal activity against Aedes (Ae.) aegypti and low cytotoxicity. Methods: The cry and cyt genes of the isolates (A21, A51, L95, L910, M29, R84, R85, R87, R89, U81 and X48) were amplified by PCR. The influence of organic matter and NaCl on the larvicidal activity was tested by bioassays. Cytotoxicity was assayed on peritoneal macrophages of BALB/c mice. Results: The cyt1 (Aa, Ab, Ba), cyt2, cry4aA, cry4Ba, cry11 (Aa, Ba, Bb) and cry10 genes were identified in all native Cuban isolates. The larvicidal activity (LC90) of seven isolates was affected by the presence of organic matter in the water, while A21, A51, L910, R84, U81 and X48 had better LC50, LC90, LC95 than the 266/2 9-VI-98 control strain. The LC50 of two isolates was affected by the presence of NaCl and A21, A51, R85 isolate had better larvicidal activity than the 266/2 9-VI-98 control strain. In terms of toxicity against macrophages, the extracts of nine isolates were less cytotoxic than the control strains. Conclusions: Native isolate A21 had the main virulence factors against Ae. aegypti larvae, displayed a good larvicidal activity in presence of different factors related with Ae. aegypti breeding sites, and had low citotoxicity against macrophages. These results can contribute to the improvement of existing biological control strategies and the development of new biolarvicides.